Adaptive Protection of Distribution Feeders Alexander Apostolov, Benton Vandiver

Introduction Requirements for reduction in the duration of short circuit faults on distribution feeders. Significant improvement in the performance of non-communications based distribution protection solutions can be achieved by the implementation of adaptive protection at the distribution level of the system. Page 2

Frequency Tracking The sampling of the input signals is synchronized to the power frequency to give a relay specific number of samples per cycle - for example 48. Close control of the sample rate improves the sensitivity and the accuracy of the protection functions. While a fault is present, or when there is insufficient voltage to permit tracking, the sample rate is maintained at the last measured value.

Multiple Setting Groups The performance of the protection and control IED is affected by the power system configuration. The typical solution in the case of IEDs is by changing to a new setting group. Multiple opto-isolator inputs are dedicated to changing between setting groups.

Programmable Scheme Logic The PSL in modern multifunctional IEDs is an extremely powerful tool. Multiple instances of the same protection function can be enabled or disabled as a function of dynamic changes of the substation or power system configuration. The advantage of this approach is that it is instantaneous and it affects only a very limited part of the relay logic.

Analog Circuit Supervision The performance of transmission line protection relays can be significantly affected by failure in the analog circuits. In case of failure of voltage signals the relay no longer correctly measures impedance.

Analog Circuit Supervision There are three main aspects to consider regarding the failure of the VT supply. –Loss of one or two phase voltages –Loss of all three phase voltages under load conditions –Absence of three phase voltages upon line energization Current transformer supervision

Page: 8 Adapting to topology cahges

Page: 9 Voltage Transformer Supervision

Page: 10 Adapting to Fault Location

Page: 11 Adapting to Changes in Voltage (Sympathetic Trip)

Page: 12 Adapting to IED Failure (Selective Backup Tripping)

Questions? Page 13